AF showed up a week early after sex???

Kellie • Mother of three and currently ttc #4 due to health issues my chances are starting to shorten every day! Staying positive and wishing everyone lots of baby dust
AF is damn near gone.. But five days ago me and SO had sex and my period came full fledge!! I was so disappointed!! Maybe it just has changed and its now back to 28 days! So I'm back in the race.. Waiting to ovulate.. Anyone else had this happen to them?